1. Field of the Invention
The present invention relates to a polymer electrolyte membrane and a fuel cell using the same, and more particularly, to a polymer electrolyte membrane having excellent ionic conductivity and low cross-over of methanol, and a fuel cell using the polymer electrolyte membrane.
2. Description of the Related Art
Conventional fuel cells can be classified into polymer electrolyte membrane fuel cells (PEMFC), phosphoric acid fuel cells, molten carbonate fuel cells, solid oxide fuel cells, etc. according to the type of electrolyte included therein. The operating temperature of a fuel cell and the constituent materials thereof are determined by the type of electrolyte used in the fuel cell.
Fuel cells can also be classified into an external reformer type fuel cell in which fuel is supplied to an anode after being converted into a hydrogen-rich gas by an external reformer, and an internal reformer type fuel cell or direct fuel supply type fuel cell in which a fuel in a gaseous or liquid state is directly supplied to an anode.
A representative example of a direct liquid fuel cell is a direct methanol fuel cell (DMFC). In a DMFC, an aqueous methanol solution is used as fuel, and a proton exchange polymer membrane with ionic conductivity is used as an electrolyte. Accordingly, a DMFC is a type of PEMFC.
PEMFCs are small and lightweight, but can achieve a high output density. Furthermore, a power generation system can be easily formed using PEMFCs.
The basic structure of a PEMFC may include an anode (fuel electrode), a cathode (oxidizing agent electrode), and a polymer electrolyte membrane interposed between the anode and the cathode. The anode may include a catalyst layer to promote the oxidation of a fuel. The cathode may include a catalyst layer to promote the reduction of an oxidizing agent.
In a PEMFC, the polymer electrolyte membrane acts as an ionic conductor for the migration of protons from the anode to the cathode and also acts as a separator to prevent contact between the anode and the cathode. The polymer electrolyte membrane therefore requires sufficient ionic conductivity, electrochemical stability, high mechanical strength and thermal stability at its operating temperature, and thin layers of the polymer electrolyte membrane should be easily formed.
However, since conventional polymer electrolyte membranes do not have satisfactory ionic conductivity and methanol cross-over, improvements in polymer electrolyte membranes are required.